Process for preparing polyamides from a dinitrile and a ditertiary alcohol or ester of the last



Patented Feb. 10, 1953 UNITED STATES PATENT OFFICE PRQCE SS FOB. IPREPARING POLYAMIDES FROM A DIN'ITBILE AND A DITERTIARY ALCOHOL ORE'STER OF THE LAST l, Eugene Edward :M Wilmin o L, eassignorto E. L-du Font de-Nemours & ,Company, wilmington, Del .,,a corporation. .of Delaware No Drawing. Application'Janua-ry 25,1944), Serial No. 72,'774

s ,o i (o1. zeta-rs 1 ;;2 Thisinvention relates .to. a novel processfor :The objects above statedgfire .realiZQdQYithis the preparation of synthetic linearpolyamides, invention which, briefly-1 stated, comprises ,reactwhich polyamides are suitable tor-preparation of ing; ,an-lo tgenicwdinitrile with alcompoundselepted filaments, fibers, yarns, fabrics, films-and the like. from the ,gronpconsisting ,of tertiaryalcohols, and The present invention is particularly-directed to tertiary esters containing as the sole reacting -anew'method for making the fiber-formingpolygroups alcohol and ester groups, in the presence amides described in U. S.-Patents"2,'071,250and of a strong acid catalyst. --After the-reaction has 2,139,948. proceeded for a length of--time suificient-todorm Synthetic linear polyamides ofa: highenough a polymer of the desired high -molecular weight,

-m-olecular-we ight to be useful'for textile purposes a polymer, which has"thecharacteristicrecurring are generallydifficult to prepare. '*Oneof the group of a polyam-idevmay beisolatedby precipimain difficultiesresides-in the fact that veryhigh tation with water fol-lowed hy-neutralization; .iil-

temperatures and critical pressure conditions are tration and drying. -'I- his--product-may thengbe necessary during the polymerization process. For meltdry- .or.Wet -spun or-cast toform-filaments, example, when a representative polya-midasuch fibers, films, etc. byprocesses-Well known-=inthe as polyhexamethyleneadipamide, is prepared,--a art.

polymerization time uptofour or-five'hoursat :The principle; of thisnew-reaction is.,exhib ited temperatures in the vicinity of 275 C.-and pres- .a-by thefollovving general equations iormulae, sures up to and includingZSOp. s. i. are necessary. wherein the; catalyst is; a strong acid and R and Such a process, because of the heavy equipment, 2 are. divalent;organicpradicals f of.. a ir high temperaturesand the like, musto-f necessity groups, R, R and R"';- are monovalent organic be rather expensive and; therefore,--it-is obvious -radica1s freehof reacting groups, and n.;denotes that if these same-polyamidescould be-prepared ;.any Whole number:

a II I! V at roomtemperature without such special proc- 40 "The: operable dinitriles maytbeiformulatedlas essing conditions a much cheaper polymerization N('J-R- CI I, inwhich R- is a. bivalent-.-organ-ic process could, be realized placing polyamides on radicaL-preferably'selected -from :thegroupscon- V a better economic footing. sisting of bivalent-hydrocarbonradioalsand:biva- An object of this invention therefore is .to prolent heterocyclic-radicals,--oris noneexistent as in vvide a simple andeconomical process forpreparthe case of cyanogen. "The-bivalent radical joining filament-, and film-forming synthetic linear ir;1g; the nitrilegr-oups' may bealiphatic or aropolyamides. matic, cyclic-or heterocyclic,- saturated or unsatu- Another object is to prepare synthetic linear rated and maybe unsubstitutedor-substitutedhy polyamides by a polymerization reaction carried group-s which do not interfere with the linear out at substantially room temperature in conpolymer-forming-reaction. Thus,--the-- dinitrile tradistinction to the high temperatures (180- may contain;primaryalcohol-andother-unreac- 300 C.) and, hence, expensive polymerization 'tive groups, for example primary --ether,- sulfide, reaction required to form linear polyamides by ketone, ester of primary alcohol;amide,-hal9gen the processes of the prior art. These and other and the like. Specificsuitable din-itriles'by way objects will. more clearly appear hereinafter. of example are the followingz succinonitrilepglumixture of sulfuric and phosphoric acids.

taronitrile, adiponitrile, pimelonitrile, suberonitrile, azelonitrile, sebaconitrile, isophthalonitrile, phthalonitrile, 1,8-naphthalonitrile, hexahydroterephthalonitrile, beta-phenyl adiponitrile, beta-methyl adiponitrile, 4-keto-pime1onitrile, 3- nitrophthalonitrile, 1,4-dicyanobutene-2. Preferably the radical joining the nitrile groups is a bivalent hydrocarbon radical. A mixture of two or more dinitriles may be used if copolymers are desired.

Ditertiary alcohols and esters having no other functional group reactive under the conditions of this reaction are, in general, suitable for reaction with the dinitriles as described previously to produce synthetic linear polyamides. The reason for restricting this definition to tertiary esters and tertiary glycols having no other functional groups is obvious if a linear polyamide is desired,

since other functional groups would tend to induce cross-linking to give a resultant cross-linked polymeric material that would be infusible and insoluble. As suitable examples of glycols operative in the process of this invention may be mentioned:

2,7-dimethyl-2,7-octanediol 3,8-diethyl-3,8-decanedio1 4,9-dipropyl-4,9-dodecanediol 2,l-dimethyl-2,10-undecanediol 3,1 1-diethyl-3,l l-tridecanediol 2,1l-dimethyl-2,ll-dodecanediol 3,l2-diethyl-3,12-tetradecanediol 4,13-dipropyl-4,l3-hexadecanediol 1,4-bis(3'-hydroxy-3-methyl butyl) benzene An alternative group of related reactants suitable for making polyamides comprises the cyanoalcohols and the cyano-esters. Here again it is necessary that the alcohol or ester be tertiary. With this class of reactants, a self-condensation occurs under the conditions of the process of this invention and a polyamide is formed. As some examples of suitable cyano-alcohols, there may be mentioned the following:

2-hydroxy-2-methyl-6-cyanohexane 2-hydroxy-2-methyl-9-cyanononane 3-hydroxy-3-methyl-8-cyanooctane p-(3-hydroxy-3-methyl butyl) benzonitrile 2-hydroxy-2-methyl-7-cyano-5-oxaheptane Representative cyano-esters may be easily obtained by the reaction of any of the above cyanoalcohols with acid chlorides, e. g., acetyl chloride to form the corresponding acetate. Of course, it will be realized that other suitable esterification procedures well known in the art may be used.

It is-preferable to use a 1:1 mol ratio within 110% of dinitrile and glycol or diester if a relatively long-chain polymeric product is desired. If a higher ratio of one or the other is present,

: the excess constituent tends to serve as a diluent and a polymerization is restricted, since each embryonic polynzeric molecule can only grow to the extent of availability of the component present in the smaller amount.

It has been found, in general, that strong acids are useful as catalysts for the process of this invention. Examples of suitable acids are sulfuric acid, phosphoric acid, alkane sulfonic acid, formic acid, or a mixture of various acids, such as a The acid catalyst may very conveniently be used as the reaction medium.

In general, it is not necessary to heat the reagents since the reaction usually takes place spontaneously with more or less evolution of heat.

In some cases, however, where less active reactants are employed, and/or weaker acids are used as catalysts, heatin may well be advantageous. The reaction may be carried out in the range of -20 C. or lower up to C. or higher, with the optimum range 20 C. to 40 C. preferred. External cooling of the reaction mixture may be employed where volatile reactants are used or the nature of the reactants is such that external cooling is needed to keep the temperature below about 80 C.

The time of reaction required has been found to vary somewhat according to the particular glycol, diester or dinitrile used, although a few hours are sufiicient to substantially complete the reaction in most cases. The particular acid medium in which a reaction takes place may also increase or decrease the time necessary for a complete reaction. In some cases a very short period, about an hour or less, is sufiicient, although in the case of less reactive ingredients, this time of reaction may run up to as much as one or two days or more.

The order in which the reactants are mixed is not important and may be varied to suit the particular case in hand. It has been found advantageous, however, in most cases to mix or dissolv the glycol or diester in the dinitrile first and then add this mixture to the acid solvent. This, however, is not an essential step in the process and merely constitutes a convenient method for adding the reactants in equivalent amounts. It will normally not be necessary to use an additional solvent, since many glycols and diesters form a compatible solution with dinitriles and dissolve in each other completely.

It is preferred that the concentration of the reactants in the acid catalyst be rather low so that rate of reaction will not be too fast and cause gelation before the reactants have been completely added to the acid. Concentration of the reactants in the acid may be from 2 to 40% by weight based on the total weight of the reaction mixture, with the range 10 to 20% preferred.

Polyamides of this invention may be prepared in reactors constructed of or lined with glass, porcelain, enamel, silver, gold, platinum, etc., the main requirement being, of course, that the acid used in the catalyst should not react with the reactor material. This is rather important since certain metal salts have a tendency to produce a colored polymeric product and may, in fact, in hibit the reaction.

The properties of a given polyamide, of course, will vary over a considerable range depending upon the molecular weight. Average molecular weights of the polyamides are very difficult to determine because of their limited solubility in suitable solvents. However, since intrinsic viscosity gives an indication of the degree of polymerization, it is to be used hereinafter as a measure thereof. It sufices to say that, in general, the process of this invention is capable of pro- 'ducing polyamides having intrinsic viscosities varying from 0.1 up to 2.5 or higher which comprehend polyamides of filamentand film-forming ability.

The expression intrinsic viscosity denoted by the symbol used herein as a measure of the degree of polymerization of the polyamide, is defined as follows:

l J i C as C approaches 0 wherein (m) is the viscosity of the solution of the polyamid'e inmeta-cresol divided by the viscosity of 'meta-cresol per se measured in the same units at the same temperature, and C is the concentration in grams of the polyamide per 100 cc. of solution.

The following examples wherein are 'set forth preferred embodiments further illustrate the principles and practice of this invention. Parts are by weight unless otherwise indicated.

Example I A solution of 2.3 parts 2,1l-dimethyl-2,ll-dodecanediol, 1.08 parts adiponitrile in 4.8 parts of 90% formic acid is heated with refluxing for five hours. After pouring into a mixture of ice and water a white polymeric substance is obtained by filtration. The polymer is soluble in alcohol and can be reprecipitated as a fine white powder by addition of water (yield 1.1 parts). The polymer softens at 95-100 0. and can be melt spun to give fibers. The polymer is poly- (a,a,a',a'-tetramethyl) decamethylene adipamide.

Example II A solution of 2.3 parts of 2,ll-dimethy1-2,l1- dodecanediol, 1.06 parts 1,4-dicyanobutene-2 in 4.8 parts 90% formic acid is heated with refiuxing for five hours. A sticky polymer is obtained by pouring the mixture into water, however on standing the polymer turns to a nonsticky solid (yield 3 parts). The solid softens at 90-100" C. and can be melt spun to silk fibers or melt cast into transparent films. The polyamide contains an unsaturated linkage and may be cross-linked by heating with peroxides. The polymer is poly(a,a,a,a-tetram'ethyl) decamethylene muconamide.

Example III To a solution of 2,l1-dimethyl-2,ll-dodecanediol (1.15 parts) and adiponitrile (0.54 part) in 3.1 parts of glacial acetic acid is added 100% sulfuric acid (1.8 parts). The exothermic reaction is kept at 30 C. for 3 hours, at the end of which time the viscous liquid is poured into water. The polymer is dissolved in alcohol and reprecipitated by addition of water to give 1 part of white, powdery, polymeric substance. The polymer melts at 80100 C. and can be melt spun to silky fibers. The intrinsic viscosity is 0.14. The polymer I301y(a,a,a',a' tetramethyl-deeamethylene adipamide and analyzes for 8.40, 8.33% nitrogen (theoretical value 8.30%).

Example IV Using terephthalonitrile instead of adiponitrile as in Example III, a polyamide of intrinsic viscosity 0.21 is obtained.

Example V Using p-xylylene cyanide in place of adiponitrile as in Example III, a polyamide of intrinsic viscosity 0.19 is obtained.

Example VI Five parts of Z-hydroxy-2-methyl-7-cyano-5- oxaheptane are added slowly to 35 parts of 72% aqueous sulfuric acid while the temperature is kept at 20-30% C. After standing for six hours the viscous solution is poured into water and a sticky polymer precipitates out of the solution.

Example VII Five parts of B-hydroxy isobutyl cyanide are added slowly to 45 parts of concentrated sulfuric acid at -15 C. The solution thickens rapidly and is poured into water after 2; hours. The ,e-amino acid polymer remains dissolved the aqueous solution.

Copolyamides may be easily prepared by the process of this invention simply by the expedient of using two or more dinitriles with a single glycol or diester, or again by using a multiplicity of glycols or diesters with a nitril plus any combination of these reactants. In general, such copolyamides have lower melting points than the simple polyamides but their physical properties are still such that they are eminently useful for application in the textile, filmand coating arts. Their wider solubility characteristicsand lower melting points give them certain. obvious.

advantages for specialized uses.

The fiber-formin linear polyamides resulting from the process of this invention can bespun into continuous filaments in a number of ways.

One method of spinning (wet process) consists-in dissolving the polyamide in a suitable solvent: and

extruding the resultant solution through orifices into a liquid which dissolves the solvent butnot the polyamide, and continuously collecting the filaments thus formed on a suitable revolving drum or spindle. Another method (dry process) consists in extruding a solution of the-polyamide into a chamber (which may be heated) where the solvent is removed by evaporation.

Still another method (melt process) consists-inextruding the molten polyamide through orifices into a suitable atmosphere whereit congeals to a filament. In these various methods of spinning, the fiber-forming mass may be forced through the orifice by means of gas pressure or by means of a constant volume delivery pump. By similar processes known to the art the poly amides can be formed into rods, bristles, sheets, foils, ribbons, films and the like. In the various methods of forming shaped articles from fiberiormingpolyamides and particularly when this is done from solutions of the polymers, thecharacteristics of the filaments, etc. may be altered by blending the polyamides with other polyarnides, such as polyhexamethylene adipamide, orwith resins, plasticizers, cellulose derivatives, etc. As cellulose derivatives which can be blended with the polyamide solutions might be mentioned ethyl cellulose, benzyl cellulose, cellulose acetate, etc. i

As described above, many of the polyamides or" this invention may be formed intofilaments,-

fibers and the like by the process knownin the art as melt spinnning. However, in thecase-of certain polyamides which may have melting points of 300 C. and higher, it is frequently-not feasible or economical to spin at such high temperatures. When it is desired to form polymers of this type into shaped articles, it will normally be found advantageous to use the dry or wet spinning techniques. As examples of solvents which may be used to advantage in either one or both of these spinning techniques, the following may be mentioned: meta-cresol, phenol, chloral hydrate, formic acid, sulfuric acid, ethyl alcohol, alcohol/chloroform mixtures, etc.

The advantages to be derived from the practice of this invention are obvious. Low temperature polymerization simplifies the equipment and gives rise to substantial savings in operation and in plant investment. An advantage of great importance too resides in the fact that the polymeric products resulting from the process of this invention are obtained directly in the finely divided state which obviates the necessity of the usual casting and grinding with their attendant expense and difficulties.

As many widely different embodiments may be made without departing from the spirit and scope of this invention it is to be understood that the invention is to be in no wise restricted save as set forth in the appended claims.

I claim:

1. A process for producing synthetic linear polyamides which comprises reacting within the temperature range of -20 to 80 C. an organic dinitrile of the formula: NC- -R/mCN, wherein R is a divalent radical from the group consisting of hydrocarbon and unreactive heterocyclic radicals and m is a numeral from to 1, and water with a substantially moi equivalent of the dinitrile of a compound selected from th group consisting of ditertiary alcohols and carboxylic acid esters of ditertiary alcohols containing as the sole reacting groups alcohol and ester groups, in a strong acid reaction medium and continuing the reaction within said temperature range until a polymer of the desired intrinsic viscosity is produced.

2. A process for producing synthetic linear polyamide which comprises reacting within the temperature range of 20 to 40 C. an organic dinitrile of the formula: NC-Rm-CN, wherein R is a divalent radical from the group consisting of hydrocarbon and unreactive heterocyclic radicals and m is a numeral from 0 to 1, and water with a substantially mol equivalent of the dinitrile of a compound selected from the group consisting of ditertiary alcohols and carboxylic acid esters of ditertiary alcohols containing as the sole reacting groups alcohol and ester groups, in a strong acid reaction medium and continuing the reaction within said temperature range until a polymer of the desired intrinsic viscosity is produced.

3. A process for producing synthetic linear polyamides which comprises reacting within the temperature range of -20 to 80 C. substantially equal molecular proportions of an organic dinitrile of the formula: NC-Rm-CN, wherein R is a divalent radical from the group consisting of hydrocarbon and unreactive heterocyclic radicals and m is a numeral from 0 to 1, and water and a compound from the group consisting of ditertiary alcohols and carboxylic acid esters of ditertiary alcohols containing as the sole reacting groups alcohol and ester groups, in a strong acid reaction medium in which the total concentration of said dinitrile and said ditertiary compound is within the range of 2% to 40% by weight, and continuing the reaction within said 8 temperature range until a polymer of the desired intrinsic viscosity is produced.

4. The process of claim 3 wherein the total concentration of said dinitrile and said ditertiary compound is within the range of 10% to 20% by weight.

5. The process for producing a synthetic linear polyamide which comprises reacting within the temperature range of -20 to C. adiponitrile with a substantially mol equivalent of 2,11-dimethyl-2,11-dodecanediol and water in a strong acid reaction medium and continuing the reaction within said temperature range until a polymer of the desired intrinsic viscosity is produced.

6. The process for producing a synthetic linear polyamide which comprises reacting within the temperature range of -20 to 80 C. lA-dicyanobutene-2 with a substantially mol equivalent of 2,11-dimethyl-2,ll-dodecanediol and water in a strong acid reaction medium and continuing the reaction within said temperature range until a polymer of the desired intrinsic viscosity is produced.

7. The process for producing a synthetic linear polyamide which comprises reacting within the temperature range of --20 to 80 C. terephthalonitrile with a substantially mol equivalent of 2,11-dimethy1-2,1l-dodecanediol and water in a strong acid reaction medium and continuing the reaction within said temperature range until a polymer of the desired intrinsic viscosity is produced.

8. The process for producing a synthetic linear polyamide which comprises reacting within the temperature range of 20 to 80 C. p-xylylene cyanide with a substantially mol equivalent of 2,11-dimethyl-2,ll-dodecanediol and water in a strong acid reaction medium and continuing the reaction within said temperature range until a polymer of the desired intrinsic viscosity is produced.

EUGENE EDWARD MAGAT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,071,250 Carothers Feb. 16, 1937 2,457,660 Gresham et a1. Dec. 28, 1948 OTHER REFERENCES Ritter et al., Journ. American Chemical Society, vol. 70, 1948, pp. 4048 to 4050. 

1. A PROCESS FOR PRODUCING SYNTHETIC LINEAR POLYAMIDES WHICH COMPRISES REACTING WITHIN THE TEMPERATURE RANGE OF -20* TO 80* C. AN ORGANIC DINITRILE OF THE FORMULA: NC-RM-CN, WHEREIN R IS A DIVALENT RADICAL FROM THE GROUP CONSISTING OF HYDROCARBON AND UNREACTIVE HETEROCYCLIC RADICALS AND M IS A NUMERAL FROM 0 TO 1, AND WATER WITH A SUBSTANTIALLY MOL EQUIVALENT OF THE DINITRILE OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF DITERTIARY ALCOHOLS AND CARBOXYLIC ACID ESTERS OF DITERITARY ALCOHOLS CONTAINING AS THE SOLE REACTING GROUPS ALCOHOL AND ESTER GROUPS, IN A STRONG ACID REACTION MEDIUM AND CONTINUING THE REACTION WITHIN SAID TEMPERATURE RANGE UNTIL A POLYMER OF THE DESIRED INTRINSIC VISCOSITY IF PRODUCED. 